RPS6KA1 (ribosomal protein S6 kinase, 90kDa, polypeptide 1) is also called RSK1 and is activated by mitogenic stimuli via the pathway involving the extracellular signal-regulated kinase (ERK) subfamily of mitogen-activated protein (MAP) kinases. ERK1/ERK2 is activated by MAP kinase kinase (MEK), which is in turn is activated by Raf kinase cascade initiated by GTP-bound form of Ras. The activated ERK1/ERK2 phosphorylates RSK1 and activates it. Activated RSK1 phosphorylates various substrates including transcription factor c-Fos, the cAMP response element binding protein (CREB), the transcriptional inhibitor IKB, the estrogen receptor and the kinase Myt 1, and has been implicated in cell proliferation, differentiation and survival. RSK1 also phosphorylates p27 at T198 and increases RhoA-p27 binding, resulting in inhibition of RhoA and an increase in cell motility.
